The electronics industry has been expanding rapidly due to the advent of solid-state components and the fabrication techniques necessary to incorporate these components into electrical equipment. Because of the demand, there has been extensive research directed towards finding new techniques for producing some of these components, including printed circuit boards. This research has included attempts to employ polymers and metal coated polymers in the fabrication of printed circuit boards because such polymers offer potentially attractive advantages.
One of the techniques for depositing metal onto a polymer substrate is electroless plating. In a conventional electroless plating process, the polymer substrate is acid-etched and then activated for metal deposition, usually with a mixture of tin salts and noble metal salts applied jointly or consecutively. The activated substrate is then immersed in an electroless plating bath, typically containing metal ions and a reducing agent, and metal plates onto the substrate. Selective deposition of metal can be achieved by selective activation of the substrate. A survey of the patent and technique literature relating to electrolessly plating metal onto polymers is contained in Domino, F. A., "Plating of Plastics--Recent Developments," Chemical Technology Review No. 138, Noyes Data Corp., New Jersey (1979).
Although selective deposition of metal onto polymers has been accomplished by a number of techniques, previously employed techniques suffer from significant disadvantages. For example, photolithographic and etching techniques, which have been traditionally used to prepare conductive patterns from metal-coated polymers, are relatively expensive, cumbersome and time-consuming operations. On the other hand, selective activation of polymer substrates often employs stamps or stencils containing suitable redox reagents which reduce an activating metal ion on the surface of the substrate. Although such selective activation is possible, the resolution of the metal pattern is severely limited by the physical dimensions of the stamp or stencil employed.